"nobody will check passports"

"Those are random spot checks"

So there are random spot checks where people will check passports. So "nobody will check passports" is false.

Fine, word lawyer, "nobody will check passports above the base rate of passport checking you may get anywhere, including any random trip".

If you're going to risk your future permanent residency, it is very important to know exactly what that 'base rate' is. As someone who travels a fair bit within Schengen, I can tell you that the rate is quite high, much higher than it was a few years ago. And if you happen to look "un-European", the rate is quite a bit higher.

Not "passport", valid ID. Which can be required also when not crossing a border, so you should have one.